Pizzicato - Arco

When writing for string instruments I would sometimes like to use the pizzicato. Now I know how to make this work, also in the MIDI recording. I choose pizzicato, and from then the system plays pizizcato. When I want to set i back to the usual play with the bow I use the command "arco". But it don't work. Once I set the instrument to pizzicato all the following passages are played as pizzicato, no matter how often I try to set it back to "arco". What's wrong ? I take both commands from the same box. The command pizz. works, the command arco does not.